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Depositional and diagenetic processes in the formation of the Eocene Jackson Group bentonites, Gonzales County, TexasMichaelides, Michael Nicholas 17 February 2012 (has links)
Bentonite clays are exposed in Paleogene strata stretching over 650 km parallel to the Texas coastline. This study focuses on a white and blue and a yellow and brown commercial Ca-montmorillonite bentonite near the city of Gonzales, Gonzales county, Texas. The deposits have stratigraphic ages of Late Eocene (~36.7 - 32.7 Ma). The bentonites in these deposits have varying colors, purities and brightness affording them diverse industrial uses. The distribution and geologic character of the high purity white and blue bentonite suggests that the deposit represents an accumulation of volcanic ash in a secondary tidal channel during the ash-fall event. A low rate of terrigenous clastic sedimentation and rapid accumulation of fresh ash were critical to the formation of high purity clay. The lower purity yellow and brown bentonites appear to have a fluvial origin marked by higher rates of detrital sedimentation and episodic accumulation of clay and ash.
The bentonite and associated strata were studied using optical microscopy, SEM, XRD and REE analyses to constrain their textural, mineralogic, and chemical character.
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Eocene pyroclastic volcanism is well documented from sources in southwestern North America, specifically in the Sierra Madre Occidental (Mexico), Trans-Pecos (Texas) and Mogollan-Datil (New Mexico) volcanic fields. Projected Eocene wind patterns support this region as a potential source for the Gonzales bentonites. A comparison of the trace and REE fingerprints of the white and blue bentonites and the yellow and brown bentonites with data available for Late Eocene volcanics in the North American Volcanic Database provides a couple of potential matches. The strongest potential match for the Late Eocene bentonite protolith is described as a sample of silicic tuff with an age range of 32.2 – 30.6 Ma, located in the southern Mexican state of Oaxaca. While the trace and REE match is strong, the tuff is somewhat young compared to the Jackson Group sediments. In addition, the sample location is due almost directly south of the Gonzales deposits, rather than the western location expected for a Gonzales bentonite source. The other potential matches are located in New Mexico, and the Mexican state of Chihuahua. These potential matches only have 6 REE available for comparison, and require further investigation. Many Paleogene volcanic units in southern North America are undocumented with regard to REE data or precise absolute ages. As additional geochemical analyses become available for a more extensive suite of Paleogene volcanic units, stronger matches with Gulf of Mexico Basin bentonites are expected to emerge. / text
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Experimentelle Untersuchung zur Auflösungskinetik von Kaolinit und Montmorillonit in Anwesenheit von Sulfat, Phosphat, Amino- und Carbonsäuren sowie Harnstoff im offenen und geschlossenen System / Experimental study on the dissolution kinetics of kaolinite und montmorillonite in the presence of sulfate, phosphate, amino and carboxylic acids as well as urea in open and closed systemsHillebrecht, Jens 27 October 2005 (has links)
No description available.
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Híbridos da montmorillonita-KSF contendo grupos alquiamina - Sintese, caracterização e aplicações adsortivasSilva, Márcia Maria Fernandes 04 November 2011 (has links)
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Previous issue date: 2011-11-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The sodium montmorillonite-KSF (KSF-Na+) was organically modified by intercalation reactions, ion exchange and silanization using amines and amino silanes. The solids were characterized by various techniques of X-ray diffraction, infrared spectroscopy, elemental analysis (CHN), thermogravimetry, scanning electron microscopy and nuclear magnetic resonance of 29Si and 13C. The solid chlorinated indicated the immobilization of 0.97 mmolg-1 of chlorine in the matrix KSF-Na+. The reaction of the solid precursor and chlorinated with diamines in aqueous solution and without solvent was more efficient with the molecule of ethylenediamine. Substrates containing a silanized aminosilanos with two nitrogens indicated 1.47 and 1.13 mmolg-1 groups immobilized on the matrix KSF-Na+, respectively. For reactions with increasing chain diamines (H2N ((CH2) nNH2) where n = 8, 9, 10 and 12) it was realized that nonildiamina showed better incorporation into the matrix KSF-Na+. The synthesis of solid dodecylamine saw the entry of a 2,12 mmolg-1 of organic groups, and the matrix applied to the retention of copper ions (II) with values of 115.0, 80.06, 71.16 and 62.26 mg g-1 at 303, 308, 313 and 318 K, respectively. For diamines (H2N ((CH2) nNH2) where n = 8, 9, 10 and 12) there was protonated by the set of characterizations the effectiveness of the reactions. The solid containing protonated dodecylamine (KSF-C12N+) was applied to the adsorption of the dye Remazol Brilliant Blue R 303, 313 and 323 K, other words, the adsorptive process followed the pseudo second order model. The maximum retention capacities were 27.28, 28.84 and 31.87 mg/g at temperatures of 303, 313 and 323 K, respectively, and the process is adjusted to the Langmuir model. / A montmorillonita-KSF sódica (KSF-Na+) foi organicamente modificada por reações de intercalação, silanização e troca iônica utilizando aminas e silanos aminados. Os diversos sólidos foram caracterizados pelas técnicas de difratometria de raio-X, espectroscopia na região do infravermelho, análise elementar (CHN), termogravimetria, microscopia eletrônica de varredura e ressonância magnética nuclear de 29Si e 13C. O sólido clorado indicou a imobilização de 0,97 mmolg-1 de cloro na matriz KSF-Na+. A reação do sólido precursor e clorado com as diaminas em meio aquoso e sem solvente foi mais eficiente com a molécula do etilenodiamino. Os suportes silanizados com aminosilanos contendo um e dois nitrogênios indicaram 1,47 e 1,13 mmolg-1 de grupos imobilizados na matriz KSF-Na+, respectivamente. Para as reações com diaminas de cadeia crescente (H2N ((CH)nNH2) onde n= 8, 9, 10 e 12) percebeu-se que nonildiamina apresentou melhor incorporação na matriz KSF-Na+. A síntese do sólido com dodecilamina houve a entrada de 2,12 mmolg-1 de grupos orgânicos, sendo a matriz aplicada na retenção de íons de cobre (II) cujos valores foram de 115,0; 80,06; 71,16 e 62,26 mg g-1 a 303, 308, 313 e 318 K, respectivamente. Para as diaminas (H2N ((CH)nNH2) onde n= 8, 9, 10 e 12) protonadas observou-se pelo conjunto de caracterizações a efetividade das reações. O sólido contendo dodecilamina protonada (KSF-C12N+) foi aplicado na adsorção do corante azul de remazol RN a 303, 313 e 323 K, ou seja, o processo adsortivo seguiu o modelo de pseudo segunda ordem. As capacidades máximas de retenção foram de 27,28; 28,84 e 31,87 mg/g nas temperaturas de 303, 313 e 323 K, respectivamente e o processo se ajustou ao modelo de Langmuir.
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Síntese, caracterização e aplicação em fotocatálise de nanocristais semicondutores de sulfeto de cádmio suportados em argila tiolada / SYNTHESIS, CHARACTERIZATION AND APPLICATION IN PHOTOCATALYS OF SEMICONDUCTOR CADMIUM SULFIDE NANOCRYSTALS SUPPORTED ONTO THIOLATED CLAY.Nascimento, Cristiane da Cunha 11 March 2011 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The challenge of nanotechnology, the science that studies the phenomena as well as the manipulation of materials at nanoscale (1-100 nm) is the control of composition, shape and size of nanoparticles, parameters that influence the physical, chemical, optical
and electronic properties. In this context, the so-called quantum dots (QDs) are semiconductor nanoparticles which have attracted considerable attention due to their
heavily size-dependent optical and electronic properties. Cadmium sulfide (CdS) QDs exhibit important photoluminescent properties, allowing applications in optoelectronic systems, photocatalysis, photodegradation of pollutants in the water medium etc. In this work, we present the results of the synthesis and characterization of CdS nanocrystals,
in the absence and in the presence of doping Mn (II) ions, supported on Montmorillonite thiolated (MT) as well as their application as photocatalysts. The materials were characterized by UV-Vis absorption spectroscopy, X-ray diffractometry, photoluminescence spectroscopy and High-Resolution transmission electron
microscopy. The effects of nanoparticle size, evaluated first by UV-visible spectroscopy, showed that the absorption maximum changed from 470 to 460 nm for
different proportions of the support relative to CdS precursors. The XRD patterns showed three peaks of CdS nanocrystals related to the cubic phase of CdS. The
photoluminescence spectra have shown emission bands around 470, 476, 484 and 495 viii nm, attributed to direct recombination of electron-hole pairs, and the presence of a shoulder around 578 nm, attributed to radiative recombination in trap levels from surface deffects. HRTEM images for the sample of CdS/MT 200 mg suggest the presence of monocrystalline CdS nanocrystals with approximately 4.8 nm which
assemble together forming polycrystalline aggregates with a size from about 45 nm intercalated into clay layers. The photocatalytic activity of CdS/MT and CdS:Mn / MT was studied by Rhodamine 6G (R6G) photodegradation under sunlight irradiation. The
results have shown a decrease in the intensity of the bands in addition to a shift from 526 to 505 nm in the absorption maximum with increasing time. According to the results of photocatalysis after 80min practically all the dye had been degraded, on the other hand, for the adsorption test, after the first 20 minutes there were no significant changes in the dye concentration. The rate of decolorization of dye showed that after 80 min the QDs have an effective induction in the degradation of R6G and the photocatalytic decolorization of R6G can be described by a pseudo first order kinetic model. / O desafio da nanotecnologia, ciência que estuda os fenômenos e manipulação de materiais em escala nanométrica (1-100 nm), é o controle de composição, forma e tamanho de nanomateriais, parâmetros que influenciam as propriedades físicas, químicas, óticas e eletrônicas. Dentro desse contexto, os quantum dots (QDs) são nanopartículas semicondutoras que têm atraído uma atenção considerável devido as suas
propriedades ópticas e eletrônicas, que são fortemente dependente da sua dimensão. Os QDs de sulfeto de cádmio (CdS) apresentam importantes propriedades de
fotoluminescência, que possibilitam aplicações em sistemas optoeletrônicos, nanosemicondutores, fotocatálise, fotodegradação de poluentes na água etc. Neste trabalho, apresentamos os resultados da síntese, caracterização e aplicação em fotocatálise e adsorção dos nanocristais de CdS, na presença e na ausência de dopagem com íons Mn (II), suportados em Montmorilonita Tiolada (MT). Os materiais obtidos
vi foram caracterizados por Espectroscopia de Absorção no UV-vis, Difração de Raios-X, Fotoluminescência e Microscopia Eletrônica de Transmissão de Alta Resolução. Os efeitos do tamanho das nanopartículas foram estudas por espectroscopia de UV-visível que mostraram uma absorção máxima em 470 e 460 nm para diferentes proporções da MT. Os difratogramas indicaram três picos relacionados às nanopartículas do CdS que corresponde a fase cúbica do CdS, o que foi corroborado com os dados de HRTEM. Os espectros de fotoluminescência mostram bandas de emissão em torno de 470, 476, 484 e 495 nm atribuídas à recombinação direta dos pares elétron-buraco, e a presença de um ombro em torno de 578 nm, atribuída a recombinação radiativa em níveis de armadilhas
provenientes de imperfeições do material. As imagens de HRTEM para a amostra de CdS/MT 200 mg sugerem a presença de nanocristais de CdS monocristalinos, com
diâmetro de aproximadamente 4,8 nm, agregados na forma de partículas policristalinas com um tamanho aproximadamente entre 45 nm intercalados nas lamelas da argila. A atividade fotocatalítica do CdS/MT e do CdS:Mn/MT foi estudada através da fotodegradação da Rodamina 6G (R6G) sob irradiação solar.Os resultados evidenciaram uma diminuição da intensidade das bandas e um deslocamento de 526 para 505 nm do
máximo de absorção com o aumento do tempo, indicando a formação de intermediários de degradação. De acordo com os resultados de fotocatálise, após 80min de reação praticamente, praticamente todo o corante havia sido degradado, enquanto que para o
ensaio de adsorção após os 20 primeiros minutos não houve mudanças significativas na concentração do corante nas amostras. A taxa de descolorização do corante mostrou que, depois de 80 min, os QDs tiveram uma efetiva indução na degradação da R6G e que a descoloração fotocatalítica da R6G pode ser descrita por um modelo cinético de pseudo primeira ordem.
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Síntese e caracterização de nanocompósitos do tipo polímero/silicatos lamelares com propriedades anisotrópicas via polimerização RAFT em emulsão / Synthesis and characterization of polymer/layered silicate nanocomposites with anisotropic properties via RAFT emulsion polymerizationRafael Caetano Jardim Pinto da Silva 27 September 2013 (has links)
Nos últimos anos, a incorporação de partículas inorgânicas em uma matriz polimérica com a finalidade de se obter sistemas híbridos orgânico/inorgânico utilizando diferentes técnicas de polimerização tem recebido grande atenção. Neste sentido, preservar e controlar as propriedades físico-químicas das partículas inorgânicas torna-se essencial para manter a integridade destas em nanoescala, bem como para obtenção de dispersões uniformes, magnificando os efeitos de reforço e demais ganhos de propriedades desejadas para a matriz polimérica. Quando se utiliza partículas inorgânicas anisotrópicas tais como a montmorilonita, silicato lamelar mais utilizado para obtenção de nanocompósitos do tipo polímero/silicato lamelar, este controle apresenta-se como um problema particularmente desafiador. Nesse contexto, a polimerização radicalar controlada (PRC) vem se destacando como uma importante via para atingir os objetivos mencionados acima, encontrando-se na literatura diversas estratégias de síntese em meio a solventes orgânicos na qual a efetiva nanoencapsulação de partículas inorgânicas dá-se por meio do crescimento de cadeias poliméricas na superfície destas estruturas inorgânicas. Entretanto, poucos trabalhos são encontrados envolvendo rota de obtenção semelhante em meio aquoso, tais como suspensão, emulsão e miniemulsão, processos estes que possuem grande interesse industrial, ambiental e viabilidade real de ampliação de escala quanto à produção.Desta forma, o objetivo deste projeto de pesquisa concentra-se na síntese e na caracterização de nanocompósitos do tipo polímero/silicato lamelar via polimerização radicalar controlada em emulsão. As polimerizações radicalares controladas de estireno em emulsão, via mecanismo de transferência reversível de cadeia por adição-fragmentação (RAFT), foram conduzidas na presença de argila montmorilonita (MMT) e mediadas por dois macroagentes de transferência de cadeia com grupo funcional tri-tioéster, sendo o primeiro constituído de cadeia polimérica não iônica de monoetil éter de poli(etilenoglicol) (MPEG-CPP) e outro derivado do MPEG-CPP contendo adicionalmente um bloco ionizável de poli(ácido metacrílico) incorporado à cadeia polimérica (MPEG-b-PMAA-CPP). Foram avaliados inicialmente os parâmetros de adsorção dos macroagentes MPEG-CPP e MPEG-b-PMAA-CPP na superfície da MMT bem como a influência das variáveis do processo de polimerização na adsorção dos macroagentes na MMT e na estabilidade coloidal dos complexos macroagente RAFT / MMT formados. Posteriormente foram avaliados os efeitos do pH, das concentrações dos macroagente RAFT e de MMT, bem como do tipo de iniciador na cinética de polimerização em emulsão \"ab-initio\" de estireno, conduzidas na ausência de surfatantes. As técnicas utilizadas nos estudos de adsorção e para a caracterização das argilas, dos látices híbridos e dos materiais nanocompósitos incluem: espectroscopia de UV-vis, espalhamento dinâmico de luz (DLS), espalhamento eletroforético de luz (ELS), cromatografia de permeação em gel (GPC), análise termogravimétrica (TGA), calorimetria diferencial de varredura (DSC) e microscopia eletrônica de transmissão (TEM). / In recent years, the incorporation of inorganic particles in a polymer matrix in order to obtain hybrid organic/inorganic systems using different polymerization techniques have received great attention. In this sense, preserve and manage the physical and chemical properties of inorganic particles is essential to maintain its integrity at the nanoscale, as well as to obtain uniform dispersions of them, magnifying the effects of reinforcement and other desired properties into the polymer matrix. When using anisotropic inorganic nanoobjects such as montmorillonite, the most used layered silicate to obtain polymer / layered silicate nanocomposites, this control is presented as a particularly challenging problem. In this context, the controlled radical polymerization (CRP) has been highlighted as an important way to achieve the goals mentioned above, several strategies of organic solvent-borne synthesis can be found in literature in which the effective nanoencapsulation of inorganic particles is given by through the growth of polymer chains on the surface of these inorganic structures. However, few works are found involving obtaining similar route in water-borne, such as suspension, emulsion, miniemulsion, these procedures have great interest in industrial, environmental and actual feasibility of expanding scale in manufacture. Thus, the objective of this research project focuses on the synthesis and characterization of nanocomposite-type polymer / layered silicate via controlled radical polymerization in emulsion media. The controlled radical polymerizations in emulsion, via transfer mechanism for the reversible addition-fragmentation chain (RAFT) have been conducted in the presence of montmorillonite clay (MMT) and mediated by two macroRAFT agents with functional tri-thioesters groups, being the first one constituted by a nonionic poly(ethylene glycol) methyl ether polymeric chain (MPEG-CPP) and the second on being MPEG-CPP derived but containing additionally an ionizable block of poly(methacrylic acid) inserted to its polymeric chain. The parameters of adsorption of MPEG-CPP and MPEG-b-PMAA-CPP agent on the surface of MMT as well as the influence of the polymerization process variables on the adsorption of PEO-RAFT in MMT and colloidal stability of the complex formed macroRAFT agents / MMT were firstly evaluated. Subsequently, the influence of pH, macroRAFT agents and MMT concentrations as well as the type of initiator on the kinetics of RAFT emulsion polymerization were equally evaluated. The techniques used the for adsorption studies and characterization of clays, latexes of hybrid materials and nanocomposites include: UV-vis spectroscopy, dynamic light scattering (DLS), electrophoretic light scattering (ELS), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC) and transmission electron microscopy (TEM).
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Estudo da estrutura e determinação das propriedades físico-químicas de suportes e catalisadores a base de Mg, Al e ZnFonseca, Carla Grijó 28 July 2017 (has links)
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Previous issue date: 2017-07-28 / Os argilominerais esmectítios, tais como a montmorilonita, combinam uma ampla gama de propriedades físico-químicas que resultam em elevada capacidade de adsorção. Estes incluem alta área superficial, propriedades de expansão e hidratação, bem como ampla capacidade de troca catiônica. Essas características abriram caminho para inúmeras aplicações importantes das argilas esmectitas como catalisadores heterogêneos, nanocompósitos polímero-argila, agentes de controle reológico ou para tratamento de água. A estrutura molecular lamelar de uma esmectita consiste em uma folha octaédrica intercalada entre duas folhas tetraédricas, que são principalmente feitas de ambientes AlO6 e SiO4, respectivamente. As estruturas moleculares dos argilominerais são particularmente difíceis de estudar devido aos pequenos tamanhos de cristalitos, heterogeneidade morfológica e estrutural, composições moleculares variáveis e a complexidade de sua estrutura de lamelas. A investigação teórica dos espectros de RMN de 23Na dos possíveis sinais de Na+ pode gerar informações sobre a estrutura das lamelas em termos das substituições isomórficas. Apesar dos íons Na+ estarem no espaço intercalar, suas posições são sensíveis às substituições isomórficas nas lamelas. As mudanças estruturais levam a diferentes valores de parâmetros magnéticos do núcleo 23Na (mudança química, constante de acoplamento quadrupolar e fator de assimetria) e dos espectros de RMN desses materiais. Os parâmetros de RMN de 23Na calculados e espectros simulados sugerem que Na+ pode ser uma boa sonda para investigar a estrutura lamelar destes compostos. A forma do espectro de 23Na é mais sensível às substituições isomórficas na lamela do que os outros núcleos, 27Al e 29Si. Um estudo teórico dos diferentes graus de hidratação foi realizado utilizando cálculos baseados em DFT com vários funcionais de troca e correlação. As interações fracas entre as moléculas de água e as lamelas sugerem a necessidade de correções de dispersão para simular corretamente o espaçamento basal e os potenciais termodinâmicos para o processo de desidratação. A existência das estruturas da montmorilonita (Mt) com cátion Na+ em geometria plana, representativa do modelo de uma camada de água e geometria octaédrica em um modelo com duas camadas de água foi confirmada. Os estágios da desidratação de Na+-Mt foram avaliados por cálculos termodinâmicos levando a uma boa descrição dos resultados experimentais provenientes de TG/DTG. As superfícies de Mt ativadas por ácido foram simuladas e a reatividade dos sítios AlV foi verificada por meio da adsorção de monóxido de carbono e os dados confirmam a maior acidez dos locais da face (110) em relação as faces (010). O caráter ácido das superfícies é proveniente principalmente dos prótons localizados nos grupos hidroxila (HO-Si e HO-AlV). A atividade catalítica do Mt ativado por ácido também foi avaliada para reações de esterificação e as barreiras de reação foram obtidas para ambas as superfícies. Os óxidos mistos são considerados catalisadores promissores devido à facilidade de preparação, a alta área específica e o volume dos poros. Além disso, a variedade de composições que podem ser alcançadas modifica a distribuição e a força dos sítios no material e isso pode alterar significativamente as propriedades catalíticas dos óxidos mistos. Uma vez que os óxidos mistos apresentam baixa cristalinidade e, consequentemente, sua estrutura ainda não foi refinada e relatada na literatura, uma alternativa para o design de óxidos mistos usando simulações computacionais pode ser feita pela inserção de dopantes metálicos na superfície MgO(001). Foram realizados cálculos ab initio para estudar o efeito do dopante de Zn2+ na reatividade e a atividade catalítica da superfície de MgO(001) para as reações de adsorção e dissociação das moléculas de H2O, H2S, CH3CH2OH, CH3CH2SH e CH3SCH3. A análise eletrônica mostrou que o cátion Zn2+ aumentou a reatividade da superfície localmente. Todas as moléculas se dissociam em ambas as superfícies, exceto a água e etanol, que só se dissociam na superfície MgO:Zn(001), confirmando o aumento da reatividade nesta superfície. Foram calculados o ΔGxT, as barreiras de reação e as constantes de velocidade para as reações de dissociação. / Smectite clay minerals such as montmorillonites combine a wide range of physicochemical properties that result in strong adsorption capacities. These include high surface area, swelling and hydration properties, as well as strong cation exchange capacities. These characteristics have opened the way to numerous important applications of smectite clays as heterogeneous catalysts, nanocomposite organically materials, rheological control agents, or for water treatment. The layered molecular structure of a smectite sheet consists of an octahedral layer intercalated between two tetrahedral layers, which are primarily made of AlO6 and SiO4 entities, respectively. The molecular structures of clay minerals are particularly difficult to study because of small crystallite sizes, morphological and structural heterogeneity, variable molecular compositions, and the complexity of their layer structure. The theoretical investigation of 23Na NMR spectra of the possible Na+-smectites can gives new insights about the structure of the layers in terms of the isomorphic substitutions. Despite the Na+ ions are in the interlayer space, their positions are sensitive to the isomorphic substitutions in the layers. The structural changes lead to different values of magnetic parameters of the 23Na nucleus (chemical shift, quadrupole coupling constant and asymmetry factor) and the NMR spectra of these materials. The calculated 23Na NMR parameters and simulated spectra suggest that Na+ can be a good probe to investigate the layer structure. The spectra shape for 23Na is more sensitive to isomorphic substitutions in the layer than the other nuclei 27Al and 29Si. A theoretical study of the different degrees of hydration was performed using calculations based on DFT with several exchange-correlation functionals. The weak layer–water molecules interactions suggested the need of dispersion corrections to simulate correctly the basal spacing and the thermodynamic potentials for the dehydration process. The existence of the montmorillonite (Mt) structures with sodium cation in planar geometry, representative of the one-water layer model and in octahedral geometry in a two-water layer model was confirmed. The stages of the dehydration of Na+–Mt were evaluated by thermodynamics calculations leading to a good description of the results from TG/DTG studies. The acid-activated Mt surfaces were simulated and the reactivity of the AlV sites were checked by means of the carbon monoxide adsorption and the data confirm the greater acidity of the sites on the face (110) compared to the face (010). The acid character of the surfaces comes manly from the proton sites located in the hydroxyl groups (HO-Si and HO-AlV). The catalytic activity of the acid activated Mt was also evaluated for esterification reactions and the reaction barriers were obtained for both surfaces. The mixed oxides are considered promising catalysts due to the preparation facility, the high specific area and the pore volume. Moreover, the variety of compositions that can be achieved modifies the distribution and the strength of the sites in the material, and this can significantly alter the catalytic properties of the derived mixed oxides. Since the mixed oxides present low crystallinity and, consequently, their structure was not yet refined and reported in the literature, an alternative for the model design of mixed oxides using computational simulations can be done by the insertion of metallic dopants on MgO(001) surface. Ab initio calculations were performed to study the effect of the Zn2+ dopant on the reactivity and the catalytic activity of the MgO(001) surface toward molecular adsorption and dissociation reactions of the H2O, H2S, CH3CH2OH, CH3CH2SH and CH3SCH3 molecules. The electronic analysis showed that Zn2+ cation increased the reactivity of the surface locally. All molecules dissociate on both surfaces except for water and ethanol which only dissociate on the MgO:Zn(001) surface, confirming the increased reactivity in this surface. The ΔGxT, reaction barriers and the rate constants for the dissociation reactions were also computed.
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Využití molekulárních simulací při komplexní strukturní analýze vrstevnatých materiálů / Application of Molecular Simulations in Complex Structural Analysis of Layered MaterialsVeteška, Marek January 2015 (has links)
Title: Application of Molecular Simulations in Complex Structural Analysis of Layered Materials Author: RNDr. Marek Veteška Department: Department of Chemical Physics and Optics Supervisor: RNDr. Miroslav Pospíšil, Ph.D., Dept. of Chemical Physics and Optics Abstract: Techniques of molecular simulations were used together with experimental measurements (X-ray diffraction, thermogravimetry, infrared spectroscopy, elemental analysis and others) to clarify the structure properties of various types of layered materials. The structure of Zn-Al-layered double hydroxide intercalated by pyrenetetra- sulfonate acid was solved. Depending on the relative humidity, the samples showed different arrangements with three planes of water molecules and with either one or two planes of pyrenetetrasulfonate anions. At the same time considerable variability of anions arrangement was demonstrated. The adsorption behavior of natural montmorillonite and montmorillonite modified by tetramethylammonium cations in relation to aniline and phe- nol was explored. Adsorption features differed according to both the type of adsorbed molecules and the type of adsorbents. An important role was played by the plane of water molecules right above the surface which medi- ated adsorption of anilines. The water plane area was reduced by...
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Development and Investigation of High-Performance Fire Retardant Polypropylene Nanocomposites via High Energy ElectronsXiao, Dan 04 October 2017 (has links)
Polypropylene (PP) has excellent mechanical and chemical properties. Thus, it is used in a wide range of applications. However, like for most polymers, the high flammability of PP limits its application in various fields requiring specific flame-retardant standards. Some of halogenated flame retardants are restricted by European Community directives ROHs, WEEE and REACH. Now metallic hydroxides flame retardants are widely used in industry, but the high loading (about 60 wt %) seriously destroys the mechanical properties of polymeric materials. To improve the performance of flame retardant polymers, an environment-friendly electron beam (EB) technology has been successfully used in modifying flame retardant and polymer matrix.
In this work, high efficient functional intumescent flame retardants and functional surfactant are designed and prepared for EB technology. In-depth studies the thermal stability, fire behavior and mechanical properties of these flame retardant PP composites have been studied. The possible graft-linking and cross-linking mechanisms of such EB modified composites can be well established. Specially, it is shown that the novel surfactant has better thermal stability in comparison to traditionally used modifiers.
Another part of this work deals with the exploration of novel allylamine polyphosphate (AAPP) as flame retardant crosslinker for PP by electron beam (EB) treatment. Multifunctional AAPP showed unique efficient intumescent flame retardant properties. The limiting oxygen index (LOI) value and the effective melt drop resistance in UL-94 test of multifunctional flame retardant PP composites is greatly enhanced. In the cone calorimeter test, a reduction of peak heat release rate, total heat release and smoke production is achieved. Moreover, EB treatment increased the thermal stability of these designed flame retardant PP composites. Furthermore, AAPP provided an excellent quality of char residue in the combustion stage due to P−N−C and P−O−C structure. In addition, synergistic mechanism of AAPP with montmorillonite (MMT) was explored.
Finally, different EB parameters have been used to modify fire retardant polymer nanocomposites. The effects of EB treatment on thermal stability, fire behavior and mechanical properties of fire retardant PP nanocomposites have been discussed. The heat release, the production of toxic gases and the mass loss of EB modified fire retardant PP nanocomposites are delayed in accordance to the result of cone calorimeter test. Based on these results high performance fire retardant polymer nanocomposites can be developed for industrial applications such as insulated material of wire, cable, etc.
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Adsorption of Pharmaceuticals and Endocrine Disrupting Compounds using Unmodified and Surfactant Modified Palygorskite-Montmorillonite Clay Particles in Batch and Fixed Bed Column ModesTetteh, Emmanuel 04 December 2018 (has links)
No description available.
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The Role of Nanoclay on the Deformation Behavior of Polypropylene/Maleic Anhydride Modified Polypropylene Films and Fibers in Full and Partially Molten State ProcessingFujiyama-Novak, Jane Hitomi 12 November 2009 (has links)
No description available.
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